Method for producing a corrosion and high temperature resistant aluminum alloy extrusion material

ABSTRACT

The invention relates to a method for producing a corrosion resistant aluminium alloy extrusion, consisting of an alloy with the composition ≤0.30, preferably 0.05 - 0.15 % by weight of silicon, ≤0.40, preferably 0.06 - 0.35 % by weight of iron, 0.01 -1.1 % by weight of manganese, ≤0.30, preferably 0.15 - 0.30 % by weight of magnesium, ≤0.70, preferably 0.05 - 0.70 % by weight of zinc, ≤0.35, preferably 0.25 % by weight of chromium, ≤0.20 % by weight of zirconium, ≤0.25, preferably 0.05-0.25% by weight of titanium, ≤0.20% by weight vanadium ≤0.10 % by weight of copper up to 0.15 % by weight of other impurities, each not greater than 0.03 % by weight and the balance aluminium, the method comprising the steps casting the molten metal into extrusion billet a) subjecting the billet to a homogenization treatment at a holding temperature of 550 to 620 deg.C for 6 to 10 hours b) heating the billet to a temperature of 400 to 550 deg.C c) extruding the billet to a tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry of International Application No. PCT/EP2021/053784, filed Feb. 16, 2021, which claims priority to SE 2050198-7, filed Feb. 21, 2020, and SE 2050177-1, filed Feb. 17, 2020, the disclosures of which are incorporated by reference herein.

TECHNICAL FIELD

The invention relates to a process for manufacture of a high corrosion resistant aluminum alloy extrusions, especially extruded tubes intended to be used for manufacture of automotive and HVAC&R air conditioning units, such as heat exchanger tubing or refrigerant carrying tube lines, or generally fluid carrying tube lines in e.g. in the HVAC&R field. The process produces extrusions with extensively improved resistance to pitting corrosion and enhanced mechanical properties especially in bending and end-forming.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. The work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

The introduction of aluminum alloy materials for automotive heat exchange components may include applications for both engine cooling and air conditioning systems. Aluminum alloy tubing for HVAC&R applications is also increasingly used. In some air conditioning systems, the aluminum components may include the condenser, the evaporator and the refrigerant routing lines or fluid carrying lines. In service these components may be subjected to conditions that include mechanical loading, vibration, stone impingement and road/environmental chemicals (e.g. salt water environments during winter driving conditions).

SUMMARY OF THE INVENTION

The following presents a simplified summary of the present disclosure in order to provide a basic understanding of some aspects of the disclosure. This summary is not an extensive overview of the disclosure. It is not intended to identify key or critical elements of the disclosure or to delineate the scope of the disclosure. The following summary merely presents some concepts of the disclosure in a simplified form as a prelude to the more detailed description provided below.

In some embodiments, the disclosure describes a process for producing an extrudable, drawable and brazeable aluminum extrusion that has improved corrosion resistance and is suitable for use in thin wall, fluid carrying tube lines. In some embodiments, the disclosure describes an aluminum alloy tube for use in heat exchanger applications. In some embodiments, the disclosure describes an aluminum alloy with improved formability during bending and end-forming operations.

In some embodiments, the disclosure describes an aluminum extrusion with excellent extrusion resistance, drawability, formability, high strength, good brazeability and excellent corrosion resistance for automotive lines, solar collectors, macro MPE, inner grooved tube (both straight enhanced and helical inner grooved) application.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be better understood by references to the detailed description when considered in connection with the accompanying drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure. In the figures, like reference numerals designate corresponding parts throughout the different views.

For a better understanding of the present invention, there follows a detailed description thereof with reference to the attached drawings:

FIG. 1 is an embodiment of a process flow chart for making the aluminum alloy tubes in accordance with the disclosure;

FIG. 2 is an embodiment of a corrosion result for a tube A according to an embodiment of the disclosure;

FIG. 3 is an embodiment of a process route for Multi Port Extrusion, Multi Port Extrusion + Zinc Arc Spray (ZAS) or Multi Port Extrusion + Hybraz coating, in accordance with the disclosure;

FIG. 4 is an embodiment of a process route for extruded straight enhanced tube (+ ZAS) in accordance with the disclosure.

Persons of ordinary skill in the art will appreciate that elements in the figures are illustrated for simplicity and clarity so not all connections and options have been shown to avoid obscuring the inventive aspects. For example, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are not often depicted in order to facilitate a less obstructed view of these various embodiments of the present disclosure. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein are to be defined with respect to their corresponding respective areas of inquiry and study except where specific meaning have otherwise been set forth herein.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of illustration, specific exemplary embodiments by which the invention may be practiced. These illustrations and exemplary embodiments are presented with the understanding that the present disclosure is an exemplification of the principles of one or more inventions and is not intended to limit any one of the inventions to the embodiments illustrated. The invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Among other things, the present invention may be embodied as methods or devices. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. The following detailed description is, therefore, not to be taken in a limiting sense.

Aluminum alloys of the AA3000 series type have found extensive use for these applications due to their combination of relatively high strength, light weight, corrosion resistance and extrudability. The AA3000 series alloys (like AA3102, AA3003 and AA3103), however, may suffer from extensive pitting corrosion when subjected to corrosive environments, leading to failure of the automotive and HVAC&R component. To be able to meet the rising targets/requirements for longer life on the automotive and HVAC&R systems new alloys have been developed with significantly better corrosion resistance. Especially for condenser tubing, the ‘long life’ alloy alternatives have recently been developed, such as those disclosed in US-A-5,286,316 and WO-A-97/46726. The alloys disclosed in these publications are generally alternatives to the standard AA3102 or AA1100 alloys used in condenser tubes, i.e. extruded tube material of relatively low mechanical strength. Due to the improved corrosion performance of the condenser tubing the corrosion focus have shifted towards the next area to fail, the manifold and the refrigerant carrying tube lines. Additionally, the tendency towards using more under vehicle tube runs, e.g. rear climate control systems, requires improved alloys due to the more heavy exposure towards the road environment. The fluid carrying tube lines are usually fabricated by means of extrusion and final precision drawing in several steps to the final dimension, and the dominating alloys for this application are AA3003 and AA3103 with a higher strength and stiffness compared to the AA3102 alloy. The new requirements have therefore created a demand for an aluminum alloy with processing flexibility and mechanical strength similar or better than the AA3003/AA3103 alloys, but with improved corrosion resistance.

In US-A-4 357 397 there is described an aluminum alloy containing relatively high amounts of Mn, Fe and Zn apart from some quantities of Si, Cu Mg, Cr and Ti. In table 1 of this patent specification there is disclosed an aluminum alloy consisting of ,40 % by weight Mn, 0.30 % by weight Fe, 0.60 % by weight Zn, 0.15 % by weight Si, 0.02 % by weight Cu 0.02 % by weight Mg, 0.05 % by weight Cr and 0.01 % by weight Ti. This alloy is intended as a sacrificial brazing fin stock and therefor lacks optimalisation with respect to characteristics such as improved formability, especially drawability and corrosion resistance. JP2009249727A and EP2832873A1 disclose examples of methods for producing corrosion resistant aluminum alloy extrusions.

In some embodiments of the disclosure, advantages may be obtained by use of an aluminum-based alloy, that may consist of 0.05 - 0.15 % by weight of silicon, 0.06 - 0.35 % by weight of iron, 0.01 - 1.10 % by weight of manganese, 0.15 - 0.30 % by weight of magnesium, 0.05 - 0.70 % by weight of zinc, 0 - 0.25 % by weight of chromium, 0 - 0.20 % by weight of zirconium, 0 - 0.25 % by weight of titanium, 0 - 0.10 % by weight of copper, up to 0.15 % by weight of other impurities, each not greater then 0.03 % by weight and the balance aluminum.

The manganese content may be 0.01-1.10% by weight, or between 0.30-0.60 % by weight, or between 0.40 - 0.50 % by weight. The addition of manganese may contribute to the strength, however, it is a major point to reduce the negative effect manganese have with respect to precipitation of manganese bearing phases during final annealing, which contributes to a coarser final grain size.

Addition of magnesium may be made in the range of 0.05-0.30 % by weight, preferably 0.15-0.30, or 0.15 - 0.20 % by weight, may result in a refinement of the final grain size (due to storage of more energy for recrystallization during deformation) as well as improvements the strain hardening capacity of the material. In total this may mean improved formability during for instance bending and end-forming of tubes. Magnesium may also have a positive influence on the corrosion properties by altering the oxide layer. The content of magnesium may be below 0.3 % by weight, in some embodiments, due to its strong effect in increasing extrudability.

In some embodiments, the level of zinc may be kept low to make the alloy more recyclable and save cost in the cast house. Otherwise, zinc may have a strong positive effect on the corrosion resistance and may be added up to 0.70 % by weight, but the amount of zinc may be between 0.05 - 0.70 % by weight, or 0.10 - 0.30 % by weight, in some embodiments.

The iron content of the alloy may be between ≤0.40 by weight, or 0.06-0.35 % by weight, in some embodiments. In general, a low iron content, such as 0.06 - 0.18 % in weight, may be desirable for improved corrosion resistance, as it may reduce the amount of iron rich particles which generally creates sites for pitting corrosion attack. Going too low in iron, however, may be difficult from a cast house standpoint of view, and also, may have a negative influence on the final grain size (due to less iron rich particles acting as nucleation sites for recrystallization). In some embodiments, to counterbalance the negative effect of a relatively low iron content in the alloy, other elements could be added for grain structure refinement.

In some embodiments, the silicon content may be between ≤0.30% by weight, or 0.05-0.15 % by weight, or between 0.08 - 0.13 % by weight in other embodiments. In some embodiments, it may be desirable to keep the silicon content within these limits to control and optimize the size distribution of AIFeSi-type particles (both primary and secondary particles), and thereby controlling the grain size in the final product.

To improve the corrosion resistance, some addition of chromium to the alloy may be desirable. Addition of chromium, however, may increase the extrudability and may negatively influence the tube drawability and therefore, in some embodiments, the level used may be ≤0,35% by weight, 0.05-0.25%, or 0.05-0.15 % by weight.

In order to optimize the resistance against corrosion, the zirconium content may be ≤0.20% by weight, or between 0.02-0.20 % by weight, or between 0.10-0.18% by weight in some embodiments. In this range the extrudability of the alloy may not be practically influenced by any change in the amount of zirconium.

In some embodiments, further optimising of the corrosion resistance may be obtained by adding titanium. The content may be ≤0.20% by weight, or 0.05-0.25% by weight, or 0.10-0.15% by weight in some embodiments. No significant influence on the extrudability is found for these titanium levels.

In some embodiments, the copper content of the alloy may be kept as low as possible, and ≤0.10% by weight, or below 0.01 % by weight, due to the potential negative effect on corrosion resistance and also due to the negative effect on extrudability even for small additions. The disclosure describes, in some embodiments, a method for producing a corrosion resistant aluminum alloy extrusion, consisting of an alloy with the composition:

-   ≤0.30, or 0.05- 0.15 % by weight of silicon, -   ≤0.40, or 0.06 - 0.35 % by weight of iron, -   0.01 - 1.1 % by weight of manganese, -   ≤0.30, or 0.15 - 0.30 % by weight of magnesium, -   ≤0.70, or 0.05 - 0.70 %, more preferably 0.10 - 0.30 % by weight of     zinc, -   ≤0.35, or 0.25 % by weight of chromium, -   ≤0.20 % by weight of zirconium, -   ≤0.25, or 0.05-0.25% by weight of titanium, -   ≤0.20% by weight vanadium -   ≤0.10 % by weight of copper -   up to 0.15 % by weight of other impurities, each not greater than     0.03 % by weight, and the balance aluminum. In some embodiments, the     method may include; -   a) casting the molten alloy into extrusion billet, -   b) subjecting the billet to a homogenization treatment at a holding     temperature of 550 to 620 deg.C for 6 to 10 hours, -   c)heating the billet to a temperature of 400 to 550 deg.C, -   d) extruding the billet to a tube.

In the following example, an embodiment of a manufacturing process for producing the disclosed extruded tubes is described.

EXAMPLE

The alloying elements may be added into a melting furnace to obtain molten metal of the alloy chemistry shown in Table 1.

Table 1 Alloy Si Fe Cu Mn Mg Cr Zr Zn Ti Ni V Others each Others total Alloy A 0.10 0.12 -- 0.46 0.18 -- -- 0.22 ≤0.13 -- -- ≤0.03 ≤0.15

The chemical composition of the billets was determined by means of optical emission spectroscopy

The molten metal may be cast into extrusion billet. The billet may be subjected to a homogenization treatment at a holding temperature of 550 to 620 deg.C for 6 to 10 hours. The purpose of this heat treatment may be to soften billet for extruding it through the die and to reach a sufficient temperature and attain mechanical properties. If the temperature is too low, billet may be too hard to push through the press and the die could be damaged. If the temperature is too high, the surface quality of the profile may be poor and the extrusion speed may need to be reduced. Thereafter, the billet may be heated to a temperature of 400 to 550 deg. C to achieve the desired temperature. If the temperature is too low, the billet may be too hard to push, if temperature is too high, tube surface defects, such as pickup, web tearing may occur.

The billet may then be extruded to a Multi Port Extrusion, an extruded straight enhanced tube, or a base tube for Precision Drawn Tube and/or helical inner grooved tube depending on the application.

An embodiment of a process flow chart for making the aluminum alloy tubes are shown in FIG. 1 .

The billet may be preheated to temperature 450 to 500 deg with 60 to 120 deg C/meter taper (temperature gradient along the billet length) before extrusion to a tube shape, the die may be preheated to 450 to 550 deg and soaked 2 to 10 hours before using. Extrusion runout speed of the tube may be controlled to 40 to 100 m/min to get a good quality tube surface. The extruded tube may be coiled during extrusion and can be extruded to straight tube. The tube may be cooled by quenching as soon as possible when it exits the press. Runout temperature may be controlled to lower than 590 degC to attain an optimal microstructure, surface quality and mechanical properties.

The base tube may be drawn to different sizes by different outer diameters and wall reduction. The drawn tube may be produced to H112, H12, H14, H18 temper and may be annealed after drawing to O temper. The preferred annealing process may be heating to 400 to 480 degC and holding for 0 to 3 hours, or may be held for 1-3 hours in some embodiments. Annealing for 0 hours may mean putting the tubes in the furnace before the annealing temperature is reached and taking them out as the desired temperature is reached.

In some embodiments, the extrusion or drawing the tube may be coated with zinc, for example by arc spray, for corrosion protection. Zinc average load may be 3 g/m2 to 10 g/m2. Tube with zinc coating may need to be exposed to a diffusion heat treatment before delivery. The heat treatment may be made by heating the tube to 300 to 600 degC and soaking 2 to 10 hours. And zinc diffusion depth into tube wall may be 100 µm to 300 µm.

To demonstrate the improved corrosion resistance of the disclosed aluminum alloy extrusion over known prior art materials, the corrosion resistance was tested using the so-called SWAAT test (Sea Water Acetic Acid Test). The test was performed according to ASTM G85 Annex A3, with alternating 30 minutes spray periods and 90 minutes soak periods at above 98% relative humidity. The electrolyte used was artificial sea water acidified with acetic acid to a pH of 2.8 to 3.0 and a composition according to ASTM standard D1141. The temperature in the chamber was kept at 49° C. The test was run in an Ascott Salt Spray Chamber. FIG. 2 shows a corrosion result for a tube A according to an embodiment of the disclosure and a standard AA3003 alloy tube tested in SWAAT (16X1.6 mm, O temper. SWAAT test is according to ASTM G85-A3. As can be seen in FIG. 2 , the drawn tube of type A alloy produced with the process according to the disclosure has a much higher corrosion resistance than typical AA3003 alloy extrusion.

The electric conductivity of the extrusion billet after homogenization is give in Table 2. The measurement was made according to ASTM E 1004 Electromagnetic (Eddy-Current) Measurements of Electrical Conductivity to verify that the heat treatment process was done correctly.

Table 2 Specification Min Max Median Standard deviation 30 50 38 2.0 %IACS

The mechanical properties of the final tube according to the disclosure in O/H111 temper and as brazed are shown in Table 3:

Table 3 Temper O/H111 As Brazed* Yield strength R_(p0).₂ [MPa] min. 40 min. 35 Tensile strength R_(m) [MPa] min. 85 min. 80 Elongation A5 [%] min. 30 min. 25 * the post braze values depend on the brazing cycle

Testing of mechanical properties of annealed tubes were carried out on a Zwick Z100 tensile testing machine in accordance with the NS-EN -ISO 6892-1-B standard. In the testing the E-module was fixed to 70000 N/mm2 during the entire testing. The speed of the test was constant at 10 N/mm2 per second until YS (yield strength) was reached, whilst the testing from YS until fracture appeared was 40 % Lo/min, Lo being the initial gauge length.

The results show that the aluminum alloy extrusion produced with the disclosed process gives a significantly better corrosion resistance than aluminum extrusions produced according to the standard procedure.

It was found that during extrusion of the different alloys, the extrusion pressures obtained for the tested alloys were equal to or maximum 5-6 % higher compared with the 3103 reference alloy . This is regarded as a small difference and it should be noted that all alloys were run at the same billet temperature and ram speed (no press-parameter optimisation done in this test).

Surface finish after extrusion, especially on the interior of the tube, is particularly important in this application because the tube is to be cold drawn to a smaller diameter and wall thickness. Surface defects may interfere with the drawing process and result in fracture of the tube during drawing. All the alloys investigated during the tests showed good internal surface appearance.

It will be understood that certain characteristics and combinations of the disclosure, in relation to the suction tube and the capillary tube, may vary considerably while maintaining the same functional concept for the set. Consequently, it should be noted that the embodiment described in detail herein as an example is clearly subject to constructive variations, however, within the scope of the disclosure to define an expansion device in a single piece, wherein the suction line or tube and the capillary tube may be extruded in aluminum as a single profile, and since many alterations can be made in the configuration now detailed according to the requirements prescribed by law, it is understood that the present details must be interpreted in an illustrative rather than limiting manner.

In other words, the figures depict preferred embodiments for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein.

Upon reading this disclosure, those of skill in the art will appreciate still additional alternative structural and functional designs for the systems and methods described herein through the disclosed principles herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those skilled in the art, may be made in the arrangement, operation and details of the systems and methods disclosed herein without departing from the spirit and scope defined in any appended claims. 

1. A method for producing a corrosion resistant aluminum alloy extrusion, the method comprising: providing a molten alloy with a composition comprising: less than or equal to 0.30 % by weight of silicon, less than or equal to 0.40 % by weight of iron, 0.01- 0.6 % by weight of manganese, less than or equal to 0.30 % by weight of magnesium, than or equal to 0.70 % by weight of zinc, 0.05 - 0.35 % by weight of chromium, 0.02 - 0.20 % by weight of zirconium, less than or equal to 0.25 % by weight of titanium, less than or equal to 0.20 % by weight vanadium, <0,10 less than or equal to 0.10 % by weight of copper, up to 0.15 % by weight of other impurities, each not greater than 0.03 % by weight, and the balance aluminum; casting the molten alloy into an extrusion billet; subjecting the extrusion billet to a homogenization treatment at a holding temperature of 550 to 620 deg.C for 6 to 10 hours; heating the extrusion billet to a temperature of 400 to 550 deg.C; and extruding the extrusion billet to a tube.
 2. The method according to claim 1, further comprising: annealing the extruded tube by heating the extruded tube to 400 to 480 deg.C; and holding for 0 to 3 hours.
 3. The method according to claim 1, wherein the extrusion is one of a Multi Port Extrusion, an extruded straight enhanced tube, a base tube for PDT, or a base tube for a helical inner grooved tube.
 4. The method according to claim 1, wherein the alloy contains - 0.60 % by weight; of manganese.
 5. The method according to claim 1, wherein the alloy contains 0.10 - 0.30 % by weight of zinc.
 6. The method according to claim 1, wherein the alloy contains 0.08 - 0.13 % by weight of silicon.
 7. The method according to claim 1, wherein the alloy contains 0.06 - 0.18 % by weight of iron.
 8. The method according to claim 1, wherein the alloy contains 0.05 - 0.15 % by weight of chromium.
 9. The method according to claim 1, wherein the alloy contains 0.02 - 0.20 % by weight of zirconium.
 10. The method according to claim 1, wherein the alloy contains 0.10 - 0.25 % by weight of titanium.
 11. The method according to claim 1, wherein the copper content is below about 0.01 % by weight.
 12. An aluminum extrusion comprising: less than or equal to 0.30 % by weight of silicon; less than or equal to 0.40 % by weight of iron; 0.01 - 0.6 % by weight of manganese; less than or equal to 0.30 % by weight of magnesium; less than or equal to 0.70 % by weight of zinc; 0.05 - 0.35 % by weight of chromium; 0.02 - 0.20 % by weight of zirconium; less than or equal to 0.25 % by weight of titanium; less than or equal to 0.20 % by weight vanadium; less than or equal to 0.10 % by weight of copper; p to 0.15 % by weight of other impurities, each not greater than 0.03 % by weight, and the balance aluminum.
 13. The aluminum extrusion according to claim 12, further comprising a zinc coating applied via a zinc arc spray with an average load of 3 g/m2 to 10 g/m2.
 14. (canceled)
 15. The aluminum extrusion according to claim 12 further comprising a coating of zinc.
 16. The aluminum extrusion according to claim 12, wherein the aluminum extrusion contains 0.30 - 0.60 % by weight of manganese.
 17. The aluminum extrusion according to claim 12, wherein the aluminum extrusion contains 0.10 - 0.30 % by weight of zinc.
 18. The aluminum extrusion according to claim 12, wherein the aluminum extrusion contains 0.06 - 0.18 % by weight of iron.
 19. The aluminum extrusion according to claim 12, wherein the aluminum extrusion contains 0.05 - 0.15 % by weight of chromium.
 20. The aluminum extrusion according to claim 12, wherein the aluminum extrusion contains 0.02 - 0.20 % by weight of zirconium.
 21. A heat exchanger including an aluminum extrusion comprising: less than or equal to 0.30 % by weight of silicon; less than or equal to 0.40 % by weight of iron; 0.01 - 0.6 % by weight of manganese; less than or equal to 0.30 % by weight of magnesium; less than or equal to 0.70 % by weight of zinc; 0.05 - 0.35 % by weight of chromium; 0.02 - 0.20 % by weight of zirconium; less than or equal to 0.25 % by weight of titanium; less than or equal to 0.20 % by weight vanadium; ess than or equal to 0.10 % by weight of copper; up to 0.15 % by weight of other impurities, each not greater than 0.03 % by weight, and the balance aluminum. 